Generally, a railroad includes at least one pair of elongated, substantially parallel rails coupled to a plurality of laterally extending ties and which are disposed on a ballast bed. The rails are coupled to the ties by metal tie plates and/or spring clips. The ballast is a hard particulate material such as, but not limited to, gravel. Ties may be made from either concrete or wood. The ballast filled space between ties is called a crib. Concrete ties are typically spaced about twenty-four inches apart, whereas wood ties are spaced about nineteen and a half inches apart.
During installation and maintenance various operations must be performed at each tie location. For example, ballast must be “tamped,” or compressed, to ensure that the ties, and therefore the rails, do not shift. A tamping device, not surprisingly called a “tamper,” typically consists of a pair of parallel tampers mounted on a motorized vehicle structured to travel on the rails. Each tamper has at least one work head that includes a pair of elongated, vertically extending tools structured to move together in a pincer-like motion as well as being structured to move vertically. The tools, preferably, have two prongs spaced so that each prong may be disposed on opposite lateral sides of a rail. The tamper further includes a vibration device structured to rapidly vibrate the tools. In this configuration, a work head may be disposed above a worksite tie with one tool on either side of the tie. Further, the prongs of each tool may be disposed on either sides of the rail. Thus, a tool prong is disposed above, and just outside, of each corner of the rail/tie interface. At least two generally parallel tampers are used so that one work head may be placed over each rail on a single tie.
Initially, the tools are generally vertical and parallel to each other. When actuated, the tool head moves vertically downward so that the tips of the tools, i.e. the tips of the prongs, are inserted into the ballast to a predetermined depth that is, preferably, below the bottom of the tie. The tools are then brought together in a pincer-like motion thereby compressing the ballast under the tie. Actuation of the vibration assembly further compresses the ballast under the tie. Once the vibration operation is complete, the tools are returned to a substantially vertical orientation and lifted out of the ballast. The rail vehicle then advances to the next tie and the operation is repeated. Typically, a tamping operation lasts about three seconds.
It is noted that the act of advancing the rail vehicle to the next work location may be called “indexing.” Indexing may be performed one tie at a time, or multiple ties at a time. For example, some tamping machines include a set of tamping tools at the front end of the rail vehicle and another set of tamping tools at the back end of the vehicle or on a chase vehicle. After identifying a tie at the work site as the first tie, the front set of tamping tools may work upon the “odd” ties and the back set of tamping tools may work upon the “even” ties. In this situation, the tamper vehicle would index, i.e. move forward, two ties at a time. The tamper vehicle, as well as other rail installation and maintenance vehicles, typically locates the tie/rail interface by locating the tie plate that connects the rail to the tie, e.g. by utilizing a metal detector that travels beside the rail.
It is noted that, “dual” tamper in this application means two tampers per rail and not two parallel tampers disposed over parallel rails, which is typical. It is further noted that, due to the size limitations of the equipment involved, there are no single vehicle solutions that incorporate all the elements of a dual tamper vehicle. For example, different sets of tampers may not act upon adjacent ties, yet, due to the forces involved, both tampers must be disposed between, i.e. supported by, rail wheels on either side.
Thus, one set of tampers has typically been disposed on a chase vehicle. Further, between the equipment used to locate and track the positions of ties, the size of the tampers and the need for an operator cabin, a single rail vehicle would be too long to effectively operate. The traditional solution was to place certain equipment on a separate vehicle. For example, the tie locating equipment or the second pair of tampers would be located on a lead or chase vehicle.
It must also be noted that, unlike most road vehicles, rail vehicles do not have an independent suspension for each wheel. Thus, assuming a rail vehicle has a rigid frame and four wheels, if all the wheels were fixed to the rail vehicle frame assembly and if one of the rails had a low spot, e.g. a spot in need of repair, the rail vehicle may be placed in a position wherein it is supported by three of the wheels allowing a gap between the fourth wheel and the rail. There are many reasons, including safety, why this is not desirable. To address this situation, most rail vehicles have one pair of wheels, or one wheel carriage having four wheels, pivotally coupled to the rail vehicle frame and structured to pivot about a longitudinal axis (almost all rail wheels, or wheel carriages, are structured to rotate about a vertical axis so that the vehicle can travel over curves). By allowing one set of wheels to pivot about a longitudinal axis while the other set of wheels does not, causes the rail vehicle frame assembly to be, essentially, supported by three points (the minimum number of support points for stability). Thus, when such a rail vehicle travels over a low spot on a single rail, the set of wheels that may pivot longitudinally rotate relative to the frame assembly so that all the wheels stay in contact with the rails.
This configuration, however, essentially prevents the construction of segmented rail vehicles. That is, assuming the segments of the vehicle are coupled by a typical railroad vehicle coupling, any segment of a rail vehicle supported only by a set of wheels having a longitudinal pivot would simply fall over. As noted above, any segment of such a rail vehicle supported by the wheels coupled to a longitudinal pivot would be, essentially, supported by a single point which may rotate. In such a configuration, gravity would cause the frame assembly to rotate about the longitudinal pivot until the frame assembly contacted the ground or another fixed object.